John H. Woodhouse

John Woodhouse received the Inge Lehmann Award at the 2001 Fall Meeting Honors Ceremony on 12 December, in San Francisco, California. The award is given for outstanding contributions to the understanding of the structure, composition, and dynamics of the Earth’s mantle and core.

Citation

“Usually, once you receive the Macelwane Medal, that is it for AGU honors. John Woodhouse is an exception, and even then he has been selected for his second medal sooner than anyone so far. Only 17 years have passed since the meeting in Cincinnati when Freeman Gilbert read the citation for John. But these have been very good years for John and for seismology, in general. Since then, we have produced three-dimensional images of the Earth’s deep interior ranging from the crust to the inner core. We have expanded our global seismographic network from a dreamy design to the reality of well over 100 state-of-the-art stations, most of which transmit data in real time. When John and I were starting the centroid-moment tensor project in 1980, sometimes data from only several stations were available after a wait of 2, sometimes 3, months. Their small dynamic range made the analysis difficult, particularly for large events, when the ground motion exceeded the capacity of the early digital instrumentation. Today, we receive data in real time from over 70 globally distributed observatories, with all events on scale.

“These things are not unconnected. We had the courage to dream, because in the spring of 1983, the time of the earliest planning of the new network, we had the first 3-D models of the upper and lower mantle structure, and it was clear that revolution was in the making. The model of the upper mantle has little changed since then, except for the improved resolution of the details. Models of the lower mantle showed striking upwellings, now called megaplumes, which remained unexplained till today but are certain to be of significance in explaining the behavior of the Earth.

“John Woodhouse received his doctorate in Cambridge, at the famed Department of Applied Mathematics and Theoretical Physics, in 1975. His first contribution that placed him on the ‘fast track’ was a brief paper noting an error in a classical paper by Backus and Gilbert; the error was not in mathematics but in physics. Until 1976, perturbations in normal mode frequencies were calculated using wrong formulae.

“After 2 more years at Scripps and Cambridge, John joined the Harvard faculty in the fall of 1978 as an assistant professor, but he made such rapid progress that he was promoted to full professor in 4 years. From this period came classical papers on coupling of normal modes in an heterogeneous Earth, which paved the way for using splitting of normal modes in 3-D modeling of the Earth’s interior.

“John has a unique gift in his ability to formulate ‘useful theory’; there are few, if any, of his papers that did not lead to important applications in studying the Earth. One such example was the development of the CMT algorithm, and another was an ingenious application of asymptotic properties of normal modes to measuring simultaneously odd and even harmonics of the mantle heterogeneity. Together, these two developments led to a 3-D model of the upper mantle that has been little improved in the last 18 or so years.

“In the landmark year of 1986, John built the first 3-D model of shear velocity of the entire mantle, using splitting functions to derive an even-degree model of the mantle, to show that the large-scale features of heterogeneity are robust over 3 or so decades of frequency. In the same year, he demonstrated that the anomalous splitting of very high phase velocity compressional modes can be explained by anisotropy of the inner core. This was the fiftieth anniversary of its discovery by Inge Lehmann, a very appropriate tribute.

“In 1990, John returned to England to assume a professorship at Oxford. He has built there a leading group in global seismology in Europe, with excellent computational facilities and a complete data archive of global network data. He continues to provide us with fascinating glimpses of the Earth’s deep interior. One hopes that the duties of a department chair will not slow him down.

“With the flood of new data that the U.S. Array project, as a part of Earthscope initiative, will generate, we need John’s skills in developing a better theory, which will be needed to take full advantage of the high-quality, high-density mapping of the Earth’s deep interior. If everything goes well, perhaps there will be another AGU medal for John in 17 years.”

—ADAM M. DZIEWONSKI, Harvard University, Cambridge, Mass.

Response

“Madam President, Ladies and Gentlemen,

“It is a great honor and a great pleasure to receive this award.

“I would like to thank the AGU and the committee, and I also thank my colleagues who must have written quite unreasonable letters.

“To paraphrase Newton, I seem, to myself, to have been playing on the seashore, diverting myself by finding smoother pebbles (for which read tractable problems at long periods) while the ocean of truth lies undiscovered before me. And, of course, there is a vast undiscovered territory in the unknown Earth structure at shorter scale lengths, and also in the properties if seismic waves at shorter periods. A strong motion seismologist, on hearing that I was a long-period seismologist, once said to me ‘Ah—long periods. That is simple,’ to which I responded, immediately on the defensive, ‘Not the way I do it.’As Adam has said, these have been exciting years in the development of ideas about the Earth, and I feel privileged to have been a part of it. It is a particular pleasure tonight that there are many here who are friends and who have, themselves, each made contributions equally deserving of honors. I would like to thank them and to say to them how exciting and rewarding it has been to have been a coworker with you in a great endeavor in this era of dramatic progress.

“There are many factors that have led to these rapid advances. Here I would like to pay tribute to the pioneers of digital seismometry, instrumentation, recording and distribution of data. Albuquerque, IDA, Geoscope, Erlangen have led the way, and IRIS has played a key role in coordinating a global effort, which has truly revolutionized seismology. Let me also pay tribute to the senior seismologists, Adam, of course, prominent among them, who single-mindedly have pursued the vision which has led to this revolution. Peter Medawar said of James Watson, at Cambridge in the 1950s, ‘in addition to being extremely clever, he had something important to be clever about.’ The data streams now available, together with enormous computational resources, give us and future generations of geophysicists, something important to be clever about.

“Medals and honors are sometimes made to mark the end of a long career. I hope and intend that this will not be so in my case. I can take heart from the example of Inge Lehmann. It was only after her retirement at the age of 65, having discovered the inner core some 17 years earlier, that she embarked on the systematic study of upper mantle structure which resulted in the naming of the Lehmann discontinuity in her honor. She was concerned with the regional variation of this feature, and it speaks for her modernity that there are papers at this meeting reporting on this very issue. Trained in mathematics, committed to recording and acquiring data, intimately acquainted with the detailed interpretation of seismograms, Inge Lehmann was a model geophysicist of her own or any other generation.

“It is an honor indeed to receive the Inge Lehmann medal from the American Geophysical Union.”